Bogies for custom loco(s) - Hornby X8786 Collector Assembly?

[Rhydgaled]

I hope to build a fictitious diesel locomotive (and possibly two more of a similar design if I can find a way to scratch-build the bodyshells - a challenge given my current zero skill).

 

I have an early Hornby class 91 and the way the bogies clip into the chassis looks quite straightforward so I thought if I obtain some spare class 91 bogies for my new loco(s) it shouldn't be too difficult for someone (most likely my engineering-skilled brother) to build a custom chassis to accept them. However, I understand there are three (soon to be four) different versions of the 91 so I'm not sure what the best combination of components would be.

 

Two service sheets are available for the three current versions of the 91, HSS 208B and HSS 285C. Both service sheets show what appears to be a set of all-wheel wiper pickups for the unpowered bogie, but my model does not appear to have one of these and on the service sheet for the 3-pole motored version this part is not labelled with a part number. On the 5-pole version it is labelled as X8786 Collector Assembly. Am I correct in believing that purchasing one of these would upgrade the non-powered bogie X8513 from 2-wheel to 4-wheel pickup? And is X8513 identical between all existing versions of the class 91?

 

I understand there is also a version of the 91 with the new Railroad motor bogie (as found in the Railroad IC125), but I cannot find a service sheet for that. I'm not sure what the best motor to go for would be, the Railroad one, the 5-pole Ringfield or something else entirely. I note that the non-powered bogie wheelsets don't have traction tyres, but do have a gear on the axle which suggests that if I buy two non-powered bogies it would be possible to use that gear to drive the wheel from a chassis-mounted (rather than bogie-mounted) motor but I'd be completely reliant on others to sort out the gearing in that case. X7691 is apparently the motor and flywheelS from the new super-detail 91 (service sheet HSS 455 here), would that be a good option?

Edited March 15, 2021 by Rhydgaled